Bracket

a support, as of metal or wood, projecting from a wall or the like to hold or bear the weight of a shelf, part of a cornice, etc.
a shelf or shelves so supported.
Also called square bracket. one of two marks [ or ] used in writing or printing to enclose parenthetical matter, interpolations, etc.
Mathematics.

brackets, parentheses of various forms indicating that the enclosed quantity is to be treated as a unit.
(loosely) vinculum (def 2).
Informal. an expression or formula between a pair of brackets.

a grouping of people based on the amount of their income:
the low-income bracket.
a class; grouping; classification:
She travels in a different social bracket.
Architecture.

any horizontally projecting support for an overhanging weight, as a corbel, cantilever, or console.
any of a series of fancifully shaped false consoles beneath an ornamental cornice.

(on a staircase) an ornamental piece filling the angle between a riser and its tread.
Shipbuilding.

a flat plate, usually triangular with a flange on one edge, used to unite and reinforce the junction between two flat members or surfaces meeting at an angle.
any member for reinforcing the angle between two members or surfaces.

a projecting fixture for gas or electricity.
Gunnery. range or elevation producing both shorts and overs on a target.
to furnish with or support by a bracket or brackets.
to place within brackets; couple with a brace.
to associate, mention, or class together:
Gossip columnists often bracket them together, so a wedding may be imminent.
Gunnery. to place (shots) both beyond and short of a target.
Photography. to take (additional shots) at exposure levels above and below the estimated correct exposure.
Contemporary Examples

Obama’s Smart Crisis Management Howard Kurtz March 18, 2011
ESPN’s Bracket Champion Shares His March Madness Secrets Ben Teitelbaum March 17, 2014
Kelly Slater Gets a Perfect Surfing Score Mark Lukach June 11, 2013
While We’re at It, 12 More Outrages To Tax Richard Cohen March 18, 2009
After a Stunning Loss at the French Open, Tennis Star Serena Williams Is No Longer Queen Lindsay Sakraida May 31, 2012

Historical Examples

The Old Countess; or, The Two Proposals Ann S. Stephens
The Law-Breakers Ridgwell Cullum
Tripping with the Tucker Twins Nell Speed
Shavings Joseph C. Lincoln
Six Girls Fannie Belle Irving

noun
an L-shaped or other support fixed to a wall to hold a shelf, etc
one or more wall shelves carried on brackets
(architect) a support projecting from the side of a wall or other structure See also corbel, ancon, console2
Also called square bracket. either of a pair of characters, [ ], used to enclose a section of writing or printing to separate it from the main text
a general name for parenthesis, square bracket, brace (sense 6)
a group or category falling within or between certain defined limits: the lower income bracket
the distance between two preliminary shots of artillery fire in range-finding
a skating figure consisting of two arcs meeting at a point, tracing the shape ⋎
verb (transitive) -kets, -keting, -keted
to fix or support by means of a bracket or brackets
to put (written or printed matter) in brackets, esp as being irrelevant, spurious, or bearing a separate relationship of some kind to the rest of the text
to couple or join (two lines of text, etc) with a brace
(often foll by with) to group or class together: to bracket Marx with the philosophers
to adjust (artillery fire) until the target is hit
n.
v.